1. Field of the Invention
The present invention relates to a multi-layered device including a plurality of multi-layered insulator layers, and an electronic equipment that employs the multi-layered device.
2. Description of the Related Art
Conventionally, there have been proposed various multi-layered devices including multi-layered ceramic insulators and a plurality of resonators built in the layered ceramic insulators. Referring to FIGS. 9 and 10, a multi-layered device according to a prior art will be described below. FIG. 9 is an exploded perspective view of the multi-layered device according to the prior art. In addition, FIG. 10 is a sectional schematic view (a sectional view along a line B-B′ of FIG. 9) of the multi-layered device according to the prior art. It is noted that the common components are denoted by the same reference numerals.
Referring to FIGS. 9 and 10, reference numerals 901, 902, 903, 904 and 905 denote dielectric sheet layers, and an insulator 920 is constituted by multi-layering these layers. The multi-layered device includes ground electrode layers 906 and 907 arranged inside or on the surfaces of the insulator 920, substantially in parallel to the dielectric sheet layer 901, side-surface ground electrodes 912 and 913 arranged on the side surfaces of the insulator, and a plurality of resonators 921 and 922 formed in the insulator. A first resonator 921, which is one of the plurality of resonators, includes a first capacitive electrode layer 908 arranged substantially in parallel to the dielectric sheet layer 904, and a first viahole inductor conductor 914 which has one end connected to the first capacitive electrode layer 908 and is arranged to be substantially perpendicular to the dielectric sheet layer 904.
It is noted that the first viahole inductor conductors 914a and 914b of FIG. 9 are connected to each other in a shape of one straight line to constitute a first viahole inductor conductor 914 as shown in FIG. 10. In addition, a second resonator 922, which is another one of the plurality of resonators 921 and 922, includes a second capacitive electrode layer 909 arranged substantially in parallel to the dielectric sheet layer 904, and a second viahole inductor conductor 915, which has one end connected to the second capacitive electrode layer 909 and is arranged to be substantially perpendicular to the dielectric sheet layer 904. It is noted that the viahole inductor conductors 915a and 915b of FIG. 9 are connected to each other in a shape of one straight line to constitute a second viahole inductor conductor 915 as shown in FIG. 10.
The dielectric sheet 903 is sandwiched between (a) capacitive coupling electrodes 910 and 911 and (b) the first capacitive electrode layer 908 and the second capacitive electrode layer 909, and the capacitive coupling electrodes 910 and 911 are opposed to the first capacitive electrode layer 908 and the second capacitive electrode layer 909, so as to form a capacitor and to capacitively couple the plurality of resonators 921 and 922. By appropriately adjusting a combination of the capacitance of this capacitor, and a coupling coefficient value of the magnetic coupling between the first viahole inductor conductor 914 and the second viahole inductor conductor 915, desired characteristics can be obtained. It is noted that the Japanese patent laid-open publication No. JP-9-238040-A has been known as a prior art reference document relevant to the present invention.
However, the above-mentioned multi-layered device according to the prior art has such a problem that the reduction in the height of the multi-layered device results in a large insertion loss, and desired characteristics cannot be obtained when the multi-layered device is made smaller, since the magnetic coupling between the resonators becomes too strong due to a narrowed interval between the resonators. Namely, there is such a problem that the magnetic coupling becomes strong particularly when a distance between the first and second viahole inductor conductors is shorter than 1.5 times the length of the first viahole inductor conductor.
The self-inductance of a linear conductor having a radius “a” and a length “1” can be obtained by the following Equation (1), and a mutual inductance between two linear conductor having a center-to-center distance “d” can be obtained by the following Equation (2):
                    L        =                                            μ              ⁢                                                          ⁢              0                                      2              ⁢              π                                ⁢                      (                                          l                ⁢                                                                  ⁢                                  log                  (                                                            1                      +                                                                                                    a                            2                                                    +                                                      l                            2                                                                                                                a                                    )                                            -                                                                    a                    2                                    +                                      l                    2                                                              +              a                        )                                              (        1        )                                M        =                                            μ              ⁢                                                          ⁢              0                                      2              ⁢              π                                ⁢                      (                                          l                ⁢                                                                  ⁢                                  log                  (                                                            1                      +                                                                                                    d                            2                                                    +                                                      l                            2                                                                                                                a                                    )                                            -                                                                    d                    2                                    +                                      l                    2                                                              +              d                        )                                              (        2        )            
According to the Equations (1) and (2), when the radius “a” is set to 0.04 mm, the length “l” is set to 0.45 mm, and the distance “d” is set to 0.9 mm, the self-inductance becomes 0.2433 nH, mutual inductance becomes 0.022 nH, then the coupling coefficient becomes 0.091. Using these setting values, it was tried to design a filter for a wireless LAN having a bandwidth of 100 MHz at a center frequency of 2.45 GHz. In this case, the designing was performed by using an equivalent circuit based on the construction of FIGS. 9 and 10. As a result, a satisfactory characteristic as shown in FIG. 11 was obtained. In this case, the insertion loss within the band was 2.3 dB, the attenuation was 30 dB at a frequency of 1990 MHz outside of the band, and the minimum attenuation of 45 dB was obtained at a frequency of equal to or smaller than 1800 MHz.
However, when the distance “d” is set to 0.89×l, namely, when the distance “d” is set to 0.4 mm so as to reduce the size of the multi-layered device, the mutual inductance becomes 0.047 nH, and the coupling coefficient becomes 0.192. FIG. 12 shows characteristics when filter designing having specifications similar to those mentioned above is attempted by the method which is the same as the method mentioned above. It can be understood that the attenuation at the frequency of equal to or smaller than 1800 MHz becomes a minimum value of 33 dB leading to remarkable deterioration in the power transmission although the insertion loss has a satisfactory value of 2.2 dB.
Conversely, when it is tried to secure a sufficient attenuation in this frequency range, the characteristics in the passband is significantly deformed, and the insertion loss becomes larger than 3 dB. In addition, the impedance matching is also worsened, and this leads to degraded usability as a filter. As described above, the narrowed interval between the resonators inevitably causes the stronger magnetic coupling and deterioration in the performance, and this leads to a serious hindrance to promoting the size reduction.